BOG Compressor Skid Fabrication for Burckhardt Compression: BV & ABS Classification for LNG and LPG Carriers

Lmart fabricated three BOG and process-gas compressor skids for Burckhardt Compression AG — the world’s leading reciprocating compressor manufacturer — across two separate contracts spanning 2020 to 2024. The scope covered LNG carrier and LPG carrier applications under BV and ABS classification, with Lmart serving as the skid fabricator responsible for structural frames, process piping, auxiliary systems, instrumentation, and full skid integration around Burckhardt’s OEM compressor units.

Compressor OEM	Burckhardt Compression AG — Winterthur, Switzerland
Equipment	3× Compressor Skid Assemblies (BOG / process gas)
Classification	BV (Bureau Veritas) & ABS (American Bureau of Shipping)
Hull Numbers	HZS H1870A (LNG carrier); Wison Nantong (LPG carrier)
Shipyards	Hudong-Zhonghua Shipbuilding (Shanghai); Wison (Nantong) Heavy Industry
Lmart Scope	Structural frame, process piping, auxiliary systems, instrumentation, full skid integration
Delivery Period	2020 (Contract 1 — 2 units) & 2024 (Contract 2 — 1 unit)

Customer Background

Burckhardt Compression AG, headquartered in Winterthur, Switzerland, is the global market leader in reciprocating compressor technology. Founded in 1844, the company holds a dominant position in high-pressure gas compression for the oil & gas, petrochemical, and marine sectors. Its reciprocating compressors are installed aboard hundreds of LNG carriers, LPG/ethylene carriers, and FSRUs worldwide, handling boil-off gas (BOG) re-liquefaction, fuel gas supply, and cargo vapor return duties. When a shipyard or ship owner specifies “Burckhardt BOG compressor,” they are specifying the premium tier of the market.

Like most global compressor OEMs, Burckhardt engineers and assembles the compressor unit itself — the crankcase, cylinders, valves, piston rods, and control system — at its own facilities or licensed assembly sites. However, the compressor does not ship to the shipyard as a standalone machine. It must be integrated into a complete skid assembly: a structural steel frame carrying the compressor, all interconnecting process piping, lubrication and cooling circuits, instrumentation and control wiring, safety relief systems, and vibration-damping mountings. This skid is what gets lifted onto the vessel’s deck or into the engine room, connected to ship systems, and commissioned.

For LNG and LPG carrier projects built at Chinese shipyards, Burckhardt requires qualified skid fabrication partners located near the yards. The compressor unit ships from Switzerland or a regional assembly facility; the skid fabrication, piping, and final integration happen at the fabricator’s workshop in China. This model demands a fabricator who can work to OEM-specified tolerances, satisfy classification society requirements, and coordinate delivery with shipyard construction schedules — a narrow intersection of capability that few Chinese shops can credibly claim.

Challenges and Engineering Requirements

OEM/Fabricator Interface Precision

Compressor skid fabrication is fundamentally different from fabricating a standalone pressure vessel or heat exchanger. The compressor unit arrives from Burckhardt with fixed bolt-hole patterns, piping connection orientations, and nozzle positions that are not adjustable in the field. Every foundation rail, mounting pad, and piping stub on the skid must align to the OEM’s interface drawing within millimeter-level tolerances. A dimensional error on the skid frame means the compressor cannot be installed — and rework on a multi-tonne structural assembly is measured in weeks, not days.

Lmart’s engineering team worked directly from Burckhardt’s interface control documents (ICDs) and 3D model data, translating OEM specifications into fabrication drawings that account for weld shrinkage, post-weld stress relief distortion, and machining allowances. Pre-assembly dimensional checks were performed at multiple stages before the compressor unit was set onto the completed frame.

Gas-Tight Process Piping for Hydrocarbon Service

BOG compressor skids handle methane (on LNG carriers) and propane/butane mixtures (on LPG carriers) at pressures ranging from near-atmospheric suction to discharge pressures exceeding 30 bar. Every flanged joint, welded connection, and instrument tap on the skid is a potential leak path for flammable gas in a classified hazardous zone aboard the vessel. The piping system must achieve and maintain gas-tight integrity through classification society pressure testing and throughout the vessel’s 25-year service life under continuous marine vibration.

Lmart fabricated all process piping to classification-approved weld procedures, with 100% radiographic or ultrasonic examination on pressure-boundary butt welds and helium leak testing on critical joints. Socket welds and fillet welds on instrument connections received liquid penetrant testing (PT). The completed piping system underwent pneumatic testing at the classification-specified test pressure before the surveyor released the skid for shipment.

Dual Classification: BV and ABS

The two contracts required compliance with different classification societies. The 2020 LNG carrier project at Hudong-Zhonghua was classed by Bureau Veritas (BV), while the 2024 LPG carrier at Wison Nantong fell under American Bureau of Shipping (ABS). While both societies share the general framework of IACS requirements, their specific rules for machinery installations, welding approvals, material certification, and testing protocols differ in detail. A fabricator that holds approval from only one society cannot serve both projects without a re-qualification process that takes months.

Lmart maintained approved status with both BV and ABS, with current workshop approvals covering structural steelwork, pressure piping, and machinery foundation fabrication. Welding procedures and welder qualifications were maintained in parallel for both classification regimes, allowing Lmart to switch between BV and ABS project requirements without delay.

Pulsation, Vibration, and Structural Integrity

Reciprocating compressors generate significant pulsation forces in the discharge and suction piping, as well as mechanical vibration from the crankshaft and crosshead mechanism. These dynamic loads propagate through the skid frame and into every piped connection, instrument bracket, and cable tray support. A skid structure that is adequate for static loads can fail under fatigue loading if pulsation-induced stresses are not accounted for in the design.

Burckhardt’s engineering team provided pulsation study results and forced-response analysis data for each project. Lmart’s structural engineers used this data to verify that piping support spans, bracing configurations, and foundation stiffness met the OEM’s requirements for natural frequency separation from excitation frequencies. Pipe clamps, vibration dampers, and restraint brackets were positioned per the pulsation study recommendations and verified during pre-commissioning vibration measurement at the workshop.

Why Burckhardt Selected Lmart

Classification workshop approvals across multiple societies. Lmart holds active workshop approvals from BV, ABS, DNV, CCS, LR, NK, and KR for structural steelwork and pressure piping fabrication. For Burckhardt, this meant a single fabrication partner could cover both the BV-classed LNG project and the ABS-classed LPG project without sourcing from different shops — reducing qualification overhead and ensuring consistent quality standards across contracts.

Demonstrated marine skid fabrication experience. Lmart’s track record includes compressor skid packages, refrigeration skids, process module assemblies, and LNG fuel gas supply system (FGSS) components for multiple shipyard programs and major marine OEMs including Wärtsilä, TGE, and Høglund. Burckhardt’s procurement team could verify this experience against delivered equipment records rather than relying on capability statements alone.

Proximity to Chinese shipyards. Lmart’s facility in Zhangjiagang, Jiangsu Province, sits within practical logistics distance of both Hudong-Zhonghua Shipbuilding in Shanghai and Wison Heavy Industry in Nantong. This proximity simplifies pre-delivery inspections, allows Burckhardt’s site engineers to visit during critical fabrication milestones, and enables direct truck delivery to the shipyard without the risk and cost of intermediate transshipment.

Repeat engagement as the strongest form of endorsement. The 2020 contract for two BOG compressor skids was Lmart’s first direct engagement with Burckhardt Compression. The 2024 follow-on order for a third skid — a different vessel type (LPG vs. LNG), different classification society (ABS vs. BV), and different shipyard (Wison vs. Hudong-Zhonghua) — represents the kind of repeat business that only follows when the first project delivered without quality or schedule problems. OEMs of Burckhardt’s caliber do not return to fabricators who created rework or delay on the first job.

Engineering and Manufacturing Solution

Lmart’s scope on both contracts covered the complete skid assembly minus the reciprocating compressor unit itself. Burckhardt supplies the compressor — the crankcase, cylinders, piston assemblies, driver coupling, and compressor-mounted controls. Lmart builds everything around it and integrates it into a ship-ready, classification-approved package.

Structural frame fabrication. The skid base frame was fabricated from heavy structural steel sections, welded per classification-approved procedures, and stress-relieved where required by the design specification. Foundation pads for the compressor mounting were machined to flatness tolerances of ≤ 0.1 mm/m as specified in Burckhardt’s ICD. Anti-vibration mountings were installed per the OEM’s specification with documented torque values. Lifting trunnions were designed and proof-tested for the complete assembled weight including the compressor.

Process piping — gas service. Suction and discharge piping for BOG (methane) and LPG (propane/butane) service was fabricated from low-temperature carbon steel (ASTM A333 Gr.6) or stainless steel with Charpy impact testing at −46 °C or below. All butt welds in gas-carrying piping received 100% radiographic examination per classification society rules. Pipe stress analysis per ASME B31.3 confirmed nozzle loads within Burckhardt’s allowable limits. After hydrostatic testing, the piping system was dried and leak-tested with nitrogen at 1.1× design pressure, with gas detector survey of all flanged and welded joints.

Auxiliary systems. Each skid included lubrication oil supply and return piping to compressor bearings and crosshead guides, cooling water circuits for cylinder jacket and intercooler/aftercooler service, instrument air and nitrogen supply lines for pneumatic actuators and purge systems, and vent and drain piping routed to the ship’s vent mast and bilge connections. Each auxiliary circuit was individually flushed and pressure tested before integration.

Instrumentation and electrical. Field-mounted instruments — pressure transmitters, RTD temperature sensors, vibration sensors on compressor bearings, gas detectors, flow meters, and safety relief valves — were mounted, tubed, and wired to local junction boxes on the skid. Cable routing followed classification requirements for power/signal separation, with Ex-rated fittings and cable glands in hazardous area zones. All cables were tagged, terminated, and continuity-tested before shipment.

Project Breakdown: Two Contracts, Three Skids

Parameter	Contract 1 (2020)	Contract 2 (2024)
OEM Client	Burckhardt Compression AG	Burckhardt Compression AG (Order 2003772)
Quantity	2× BOG Compressor Skids	1× Compressor Skid
Vessel Type	LNG Carrier	LPG Carrier
Shipyard	Hudong-Zhonghua Shipbuilding (Hull HZS H1870A)	Wison (Nantong) Heavy Industry
Classification	BV (Bureau Veritas)	ABS (American Bureau of Shipping)
Lmart Scope	Frame, piping, auxiliaries, instrumentation, integration	Frame, piping, auxiliaries, instrumentation, integration
Delivery	2020	2024

Quality Control and Project Execution

Compressor skid fabrication under classification society oversight follows a structured inspection regime that is materially different from standard pressure vessel QC. The skid is not a single code item — it is an assembly of structural, piping, mechanical, electrical, and instrumentation components, each with its own inspection requirements and hold/witness points. Lmart’s quality team managed the following milestones across both contracts:

Material receiving inspection. All structural steel, pipe, fittings, flanges, and fasteners were inspected on receipt against classification-approved material certificates. Carbon equivalent values for structural steels were verified against the applicable BV or ABS rules for welded machinery foundations. Piping materials were checked for dimensional compliance, heat number traceability, and surface condition before entering the fabrication sequence.

Welding qualification and production control. Welding procedures for structural joints and pressure piping were approved by the respective classification society surveyor before production welding commenced. Welder qualification records were verified current for each operator assigned to the project. In-process weld inspections covered fit-up geometry, preheat compliance, interpass temperature control, and visual examination of completed welds.

Dimensional control at critical milestones. Compressor foundation bolt-hole patterns, piping flange alignment, nozzle orientations, and overall skid envelope dimensions were measured using calibrated instruments at defined hold points. Dimensional inspection reports were submitted to Burckhardt’s project engineer for review before proceeding to the next fabrication stage. For both contracts, the compressor unit was trial-fitted onto the completed frame to verify interface alignment before final bolt-up — ensuring zero-rework installation.

Non-destructive examination. Structural welds were examined per classification requirements, with the extent of RT, UT, MT, or PT determined by weld joint category and applicable Class rules. Gas service piping welds received 100% volumetric examination (RT or UT) on butt joints and surface examination (PT or MT) on fillet and socket welds. All NDT was performed by Level II qualified technicians, with reports reviewed and endorsed by the classification surveyor.

Pressure and leak testing. Process piping systems were hydrostatically tested at the classification-specified test pressure with the surveyor present at the witness point. Following hydrostatic testing, piping was dried and subjected to pneumatic leak testing with nitrogen, using gas detector survey of all flanged joints, threaded connections, and instrument taps. Test results were documented in the project quality dossier.

Final inspection and classification release. Each completed skid assembly underwent final visual and dimensional inspection by Burckhardt’s site representative and the classification surveyor. Documentation packages — including material certificates, weld maps and records, NDT reports, dimensional survey records, pressure and leak test certificates, and the classification approval certificate — were compiled, reviewed, and signed off by both parties before the skid was released for transport to the shipyard.

Results and Business Impact

All three compressor skids were delivered to the respective shipyards on schedule and accepted by both Burckhardt and the classification societies without non-conformance reports or rework. The skids were installed aboard the vessels and integrated into the cargo handling and fuel gas systems as part of each shipyard’s construction program.

The progression from the 2020 first-time contract (two BOG compressor skids for an LNG carrier under BV classification) to the 2024 follow-on order (one compressor skid for an LPG carrier under ABS classification) demonstrates earned trust. Burckhardt did not need to re-qualify Lmart for the second contract — the performance record from the first project provided the commercial and technical confidence to proceed directly. The fact that the second order involved a different vessel type, different classification society, and different shipyard makes the repeat engagement even more significant: it confirms that Burckhardt views Lmart as a versatile skid fabrication partner, not a single-project supplier.

For Burckhardt, having a reliable skid fabrication partner in China’s Yangtze River Delta shipbuilding corridor is a strategic supply chain asset. It enables them to bid on LNG and LPG newbuild programs at Chinese yards with confidence that the local fabrication scope will meet Swiss OEM quality standards and align with shipyard delivery schedules. The alternative — shipping completed skids from Europe or re-qualifying a new fabricator for each project — adds weeks of lead time and significant cost.

For the shipyards — Hudong-Zhonghua and Wison — receiving a fully integrated, classification-approved compressor skid assembly eliminates weeks of on-board fabrication work and the coordination complexity of managing piping, electrical, and structural trades in the confined spaces of an engine room or compressor room.

Customer Voice

Burckhardt Compression selected Lmart through a competitive evaluation in 2020 and returned with a second contract four years later — a pattern that speaks more clearly than any written testimonial.

“The skid fabrication quality was consistent with what we expect from our European supply chain. Dimensional accuracy on the compressor foundation was within specification on the first check, the piping system passed leak testing cleanly, and the documentation package was complete for classification sign-off. When we needed a fabricator for the Wison LPG project, Lmart was the obvious choice — we already knew what we would get.”

— Project Manager, Burckhardt Compression AG (paraphrased from project review feedback)

Note: Lmart respects client confidentiality. Specific contact references are available upon request during the qualification process.